Restore Bi-Directional text support

Summary:
Fix regression introduced by commit a565bc97 (Clip character drawing
to its own cell). When the first character in a text fragment is
classified as RTL, rest of the fragment is also considered to be RTL
and is passed to `drawText()` as one string. The rendering is not
perfect (especially when RTL and LTR characters are mixed), but it
works as before.

{F5830191}

BUG: 393644

Test Plan:
* Display example sentences using a program which prints text directly
  to terminal (e.g. `echo`, `cat`):
```
حروف به هم پیوسته

کِی‌دی‌ئی (به انگلیسی: KDE) پروژه‌ای برای توسعه یک
میزکار آزاد و متن باز است.
```
* Display the sentences in Konsole built before
  commit a565bc97
* Compare visually

Reviewers: #konsole, sassanh, hindenburg

Reviewed By: #konsole, sassanh, hindenburg

Subscribers: hindenburg, #konsole

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D12655